XCR-L Changes / Variations / Options

This post is an attempt to keep a running tab on the changes the XCR-L has gone through since it was introduced. This is a rough outline. If you have some info to add/change PM me and I'll get it in. I'm not claiming that this is the end all be all but with some input I think it'd be great to have one spot to check for guys that are new to the platform. I'll work on getting pics in and associating some of the changes with SNs. I've seen a lot of XCRs and I'm still learning about some of the changes.

"Gen" of the same number are not necessarily compatible. Ultimately it's dependent on the number of changes to the specific part.Red indicates the item is discontinued (to my knowledge).

LowerGen 1
Gen 2: Integral trigger guard added
Gen 3: Larger diameter BHO hole to use the 'M' style BHO (approx change mid 2012)
Gen 4: Gen 3 bolt compatible, large hole drilled out of the rear of the lower below the stock mounting bolt. Started in 2014, approx SN10500, will not work with Gen 1 or Gen 2 bolt. Older lowers can be modified to accept the Gen 3 bolts but will not be backwards compatible.

SafetyGen 1: Large Lever. Looks like standard AR style levers.
Gen 1: Ambi with the Large Lever. Option in the early years. Not a lot of these out there.
Gen 2: Small lever ambi. The standard since appox SN4000.

BHOGen 1: Original 2 piece.
Gen 2: One piece style with wider head.
Gen 3: Common part between M and L. Larger diameter shaft compared to Gen 2. Will not fit older lowers without some machining.(pre 2012)
StocksFixed Tube
Folding Tube
Fixed M4
Folding M4
FAST
UpperOriginal style cutout rails, quad.Picatinny style rails, quad. (Started approx 7000SN)
Shaved rails (SHOT 14, Factory option to have custom rails in the quad location)
Keymod (SHOT 14, the "standard" since introduction)
*Mini/Micro/Standard/Competition Lengths available in each config*
**Competition length only compatible with Type 3 gas block**
***Early uppers (pre 3500ish) have some extra material in between the gas tube and barrel channel that will interfere with a 300blk gas system and not allow the barrel to seat***

Gas BlockGen 1(Type 1): tool required
Gen 2(Type 2): 5 position, finger adjustable
Gen 3(Type 3): 8 position. Will fit inside the handguards. Rumored compatibility with calibers besides 300blk.
Gen 4: (rumored) short stroke piston, announced at SHOT 15, same appearance as M gas block
*Early uppers (pre 3500ish) have some extra material in between the gas tube and barrel channel that will interfere with a 300blk gas system(type 3)*
Gas TubeGen 1
Gen 2: slightly different design but otherwise compatible with previous gen.
Gen 3: for use with Gen 3 gas block/op rod in 300blk. Comes in "300 standard" and "Micro" lengths. No holes in the tubes. As of early 2016, there will be standard length versions to be used the the Type 3 gas block.
Gen 4: Rumored for the Gen4 Gas block
Op-rod/Piston headGen 1: Piston head only works with Gen 1 gas block
Gen 2: Works with Gen 2 gas block
Gen 2: Lite, longer piston head depending on gas system length, lightened the op rod slightly
Gen 3: Works with Gen 2 gas block and 300blk gas block, one piece design instead of the foot being welded on
Gen 4: Works with Gen 4 gas block(speculation, probably same rod with different piston head)
*standard, mini, micro and 300blk lengths, needs to be paired up with appropriate gas tube and gas system length*
Recoil AssyGen 1: original style
Gen 2: larger engagement surface, may be hand fit from RA. Using a gen 2 on an older lower may result in a tight or no fit between the upper and lower

Bolt Carrier
Gen 1: original style. For use on lowers prior to Gen 4.
Gen 2: for use with the combination of Gen 3 bolts and Gen 4 lowers.

BoltGen 1: Original design with original style firing pin. (Only in 5.56)
Gen 2: Upgrade, hat type firing pin. Can use Gen 1/2 interchangeably.
Gen 3: Firing pin moved to carrier. Bolt face appears the same but the shaft is shorter.

Firing PinGen 1: Original style (556 only)
Gen 2: Hat type, standard from approx SN 1000-10900
Gen 3: Used on the Gen 3 carrier. Not compatible with previous gen bolts. Larger diameter at the base, visible shoulder approx 2/3 of the way down the pin from the "hat"
Barrels
556/6.8/7.62x39/5.45x39/300blk
Std/Mini/Micro/300blk standard
Heavy/light profile
***Original barrels had a larger gas port, upgrading to the Gen 2 gas system usually resulted in an over gassed gun (IE always running on S) unless the port was modded as well.***

Do you really think we want laws to be observed? We want them broken. There's no way to rule innocent men. The only power any government has is the power to crack down on criminals. When there aren't enough criminals, one makes them. One declares so many things to be crimes that it becomes impossible for men to live without breaking laws. Who wants law-abiding citizens? Pass the kind of laws that can’t be observed, enforced, or objectively interpreted - and you create a nation of law-breakers.